#include "Plane4NodeShpFunc.h"

using SG::DataStructure::Common::Real;
using SG::Algebra::Matrixd;
using SG::FEMSolver::Element::Plane4NodeShpFunc;

Plane4NodeShpFunc::Plane4NodeShpFunc ()
:NSet (), DNDxiSet ()
{}

/** @brief 计算积分点处形函数及形函数对参数坐标导数
 * 
 * 缓存各个积分点处的计算结果，避免下一次积分点循环时重复计算（内存换取计算时间）
 */

void Plane4NodeShpFunc::Compute (const SG::DataStructure::FEM::IntegPointArray& integPoints)
{
    const auto nGauss = integPoints.size ();
    NSet.resize (nGauss);
    DNDxiSet.resize (nGauss);
    const Real quarter{0.25};
    for (std::size_t index = 0; index < nGauss; ++index)
    {
        const Real& xi{integPoints[index].m_x};
        const Real& eta{integPoints[index].m_y};

        NSet[index] = Matrixd (4, 1);
        NSet[index] (0, 0) = quarter * (1.0 - xi) * (1.0 - eta);
        NSet[index] (1, 0) = quarter * (1.0 + xi) * (1.0 - eta);
        NSet[index] (2, 0) = quarter * (1.0 + xi) * (1.0 + eta);
        NSet[index] (3, 0) = quarter * (1.0 - xi) * (1.0 + eta);

        DNDxiSet[index] = Matrixd (2, 4);
        DNDxiSet[index] (0, 0) = -1.0 * quarter * (1.0 - eta);
        DNDxiSet[index] (1, 0) = -1.0 * quarter * (1.0 - xi);

        DNDxiSet[index] (0, 1) =  1.0 * quarter * (1.0 - eta);
        DNDxiSet[index] (1, 1) = -1.0 * quarter * (1.0 + xi);

        DNDxiSet[index] (0, 2) =  1.0 * quarter * (1.0 + eta);
        DNDxiSet[index] (1, 2) =  1.0 * quarter * (1.0 + xi);

        DNDxiSet[index] (0, 3) = -1.0 * quarter * (1.0 + eta);
        DNDxiSet[index] (1, 3) =  1.0 * quarter * (1.0 - xi);
    }
}